private final int bytes;
  private final boolean supportsClone;
  private final String toString;

  MessageDigestHashFunction(String algorithmName, String toString) {
    this.prototype = getMessageDigest(algorithmName);
    this.bytes = prototype.getDigestLength();
    this.toString = checkNotNull(toString);
    this.supportsClone = supportsClone(prototype);
  }

  private final int bits;
  private final boolean supportsClone;

  MacHashFunction(String algorithmName, Key key, String toString) {
    this.prototype = getMac(algorithmName, key);
    this.key = checkNotNull(key);
    this.toString = checkNotNull(toString);
    this.bits = prototype.getMacLength() * Byte.SIZE;
    this.supportsClone = supportsClone(prototype);
  }

  @Override
  public int bits() {